Negative electrode active material for nonaqueous electrolyte battery, nonaqueous electrolyte battery, battery pack, and vehicle

ABSTRACT

A negative electrode active material contains a metal-displaced lithium-titanium oxide of a ramsdellite structure expressed by the formula Li (16/7)-x Ti (24/7)-y M y O 8  (where M is at least one metal element selected from the group consisting of Nb, Ta, Mo, and W, and x and y are respectively numbers in the range of 0&lt;x&lt;16/7 and 0&lt;y&lt;24/7).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2006-267984, filed Sep. 29, 2006,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a negative electrode active materialfor a nonaqueous electrolyte battery, a nonaqueous electrolyte batteryhaving such negative electrode active material, a battery pack, and avehicle.

2. Description of the Related Art

Conventionally, titanium oxide compounds are widely used as a negativeelectrode material for nonaqueous electrolyte lithium secondarybatteries that can be used repeatedly by charging and discharging.However, although the conventional titanium oxide compound is excellentin repeated charging and discharging characteristics, it is higher inpotential to metal lithium than graphite or other carbonaceousmaterials, and is hence lower in capacity density per unit weight.Therefore, it is low in energy density that is one of the importantproperties as secondary battery. For example, conventional titaniumoxide (anatase) is about 165 mAh/g in its theoretical capacity, and alithium-titanium composite oxide system is also about 180 mAh/g in itstheoretical capacity, both being much inferior to the theoreticalcapacity of graphite material (more than 385 mAh/g). Most of titaniumoxide compounds have few equivalent sites for inserting lithium in acrystal structure, and lithium is likely to be stabilized in itsstructure. As a result, the effective capacity becomes low. Diffusioncoefficient of lithium ion in titanium oxide is low, and thus for fastcharging and discharging, the negative electrode active material isdesired to have a higher lithium diffusion capability.

JP-A 2003-183030 (KOKAI) discloses a negative electrode active materialfor a lithium secondary battery, more specificallylithium-nickel-titanium oxide having a ramsdellite type crystalstructure represented by the formula: Li_(2-2x/3)Ni_(x)Ti_(3-x/3)O₇(0<x≦0.5). This lithium-nickel-titanium oxide is combined with divalentNi having a smaller valency than tetravalent Ti, and thus in spite ofthe ramsdellite type crystal structure, the correlation of Li—O isreinforced by the effect of Ni getting into Ti site. Therefore, athree-dimensional space suited to intercalation and deintercalation oflithium ion cannot be presented, and the diffusion performance oflithium ion is small. Hence, this lithium-nickel-titanium oxide cannotimprove the fast charging and discharging performance, in particular,among battery properties.

On the other hand, the electrode potential of titanium oxide compound isabout 1.5V on the basis of metal lithium. This electrode potential isdetermined by oxidation-reduction reaction between Ti³⁺ and Ti⁴⁺ whenintercalating and deintercalating lithium electrochemically, and cannotbe varied. Therefore, to achieve the fast charging and dischargingperformance of a secondary battery, it is important to increase thenegative electrode capacity, in addition to enhancement of diffusionperformance of lithium ion mentioned above.

JP-A 2004-221523 (KOKAI) relates to an electrochemical capacitor, inwhich the negative electrode is composed of lithium-titanium oxidehaving a ramsdellite type crystal structure, for example, Li₂Ti₃O₇. ThisLi₂Ti₃O₇ is excellent in cycle characteristics, low in risk ofovercharging among known negative electrode materials, and is known tohave excellent diffusion performance of lithium ion as compared withspinel type compound such as Li₄Ti₅O₁₂. However, this compound is low ineffective capacity (not more than 130 mAh/g) as compared withtheoretical capacity (about 230 mAh/g), and is not sufficientlyapplicable to fast charging and discharging.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided anegative electrode active material for a nonaqueous electrolyte battery,comprising a metal-displaced lithium-titanium oxide of a ramsdellitestructure expressed by the formula (1):Li_((16/7)-x)Ti_((24/7)-y)M_(y)O₈  (1)where M is at least one metal element selected from the group consistingof Nb, Ta, Mo, and W, and x and y are respectively numbers in the rangeof 0<x<16/7 and 0<y<24/7.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a structural diagram of ramsdellite type crystal;

FIG. 2 is an internal perspective sectional view schematically showing anonaqueous electrolyte battery having a coiled type battery group;

FIG. 3 is a partially magnified sectional view of the coiled typebattery group;

FIG. 4 is a partially cut-away perspective view of a nonaqueouselectrolyte battery having a laminate type battery group;

FIG. 5 is a magnified sectional view showing essential parts of thelaminate type battery group;

FIG. 6 is a perspective exploded view of the laminate type batterygroup;

FIG. 7 is a partially cut-away perspective view of a square typenonaqueous electrolyte battery according to a first embodiment;

FIG. 8 is a perspective exploded view of a battery pack according to asecond embodiment;

FIG. 9 is a block diagram of an electric circuit of the battery pack inFIG. 8;

FIG. 10 is a schematic diagram of a series hybrid vehicle according to athird embodiment;

FIG. 11 is a schematic diagram of a parallel hybrid vehicle according tothe third embodiment;

FIG. 12 is a schematic diagram of a series-parallel hybrid vehicleaccording to the third embodiment;

FIG. 13 is a schematic diagram of a vehicle according to the thirdembodiment;

FIG. 14 is a schematic diagram of a hybrid motorbike according to thethird embodiment;

FIG. 15 is a schematic diagram of an electric motorbike according to thethird embodiment;

FIG. 16 is a schematic diagram of a rechargeable vacuum cleaneraccording to a fourth embodiment;

FIG. 17 is a structural diagram of the rechargeable vacuum cleaner inFIG. 16;

FIG. 18 is a representative X-ray diffraction diagram of a ramsdellitetype compound; and

FIG. 19 is a characteristic diagram of charging and dischargingcharacteristics of a battery using the negative electrode activematerials of examples and Comparative Examples.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will be specificallydescribed below with reference to the accompanying drawings.

<Negative Electrode Active Material for Nonaqueous Electrolyte Battery>

A negative electrode active material for a nonaqueous electrolytebattery of the invention contains a metal-displaced lithium-titaniumoxide having a ramsdellite structure expressed by the formula (1):Li_((16/7)-x)Ti_((24/7)-y)M_(y)O₈  (1)where M is at least one metal element selected from the group consistingof Nb, Ta, Mo, and W, and x and y are respectively numbers in the rangeof 0<x<16/7 and 0<y<24/7.

Generally, a lithium-titanium oxide 1 having a ramsdellite type crystalstructure is formed as shown in FIG. 1, in which titanium ionscoordinate six oxygen atoms to form octahedral structures 2 of TiO₆,adjacent TiO₆ type octahedral structures 2 share an edge 3 a to formdouble chain bonds mutually, and apexes 3 b of the octahedral structures2 are coupled to one another to form a three-dimensional skeleton. Inthis skeleton shown in FIG. 1, a (2×1) tunnel is formed as indicated byreference numeral 5. The tunnel 5 functions as a space for intercalatingand deintercalating Li ions 6 in the crystal, and mainly the Li ions 6existing in the tunnel 5 are considered to contribute to charging anddischarging of a battery. Reference numeral 4 is a unit lattice. Acrystallite is formed of a set of multiple unit lattices 4. Multiplecrystallites aggregate to form a particle, and primary particles andsecondary particles are formed.

The oxide having the ramsdellite structure shown in the formula (1)increases hole sites in the tunnel 5 by displacing part of Ti ions inthis structure with cation M of larger valency than Ti ion (that is,pentavalent element M^(V) (Nb and/or Ta), and/or hexavalent elementM^(VI) (Mo and/or W)). As a result of increase of the hole sites,capacity and diffusion performance of Li ions are enhanced. That is, acorrelation of Li and O is known to be one of the important factors fordominating the diffusion of Li ions in titanium oxide compound, and byintroducing the M—O bond showing a stronger bonding strength than theTi—O bonding strength into the three-dimensional skeleton, the Li—Ocorrelation is weakened, and the diffusion performance of Li ions isimproved. Besides, by introduction of the metal element M, hole sitescapable of intercalating and deintercalating the Li ions are increased.As a result, the amount of Li that can be intercalated anddeintercalated electrochemically is increased, and thus the capacityincreases, thereby improving the Li ion diffusion performance in thecrystal structure.

The oxide expressed by the formula (1) is represented by a chemicalformula in the light of its crystal structure as shown in the followingformula (2):(Li_((12/7)-x)□_(16/7))[(Li_(4/7)(Ti_((24/7)-y)M_(y)O₈)]  (2)where the square mark indicates the hole site in the tunnel structure,and the portion enclosed by brackets [ ] represents the componentelement in the three-dimensional skeleton.

The metal-displaced lithium-titanium oxide of the ramsdellite structureexpressed by the formula (1) has an orthorhombic system or an analogouscrystal system slightly distorted from orthorhombic system, and itsrepresentative space group is Pnma showing an ideal symmetricity. Ananalogous space group slightly distorted from this representative spacegroup Pnma includes Pbnm, Pmcn, Pnmb, or Pnam. These analogous spacegroups slightly distorted from the space group Pnma include bothcomponent elements holding an ideal symmetricity, and others slightlydeviated from the symmetrical positions.

In the formula (1), x and y are desirably in the range of 0<x≦2.0, and0<y≦2.0, respectively, so that the metal-displaced lithium-titaniumoxide may be electrically neutral. If x or y exceeds 2, Li ions arealmost lost in the crystal structure, and the Li ion conductivity islowered as well as a different phase (impurity phase) may appear in thecrystal structure. To provide Li/hole ratio capable of assuring morefavorable Li ion conductivity in the metal-displaced lithium-titaniumoxide solid matter in a discharged state, x and y are more desirably inthe range of 0<x≦0.5, and 0<y≦0.5, respectively. In particular, when themetal element M is a hexavalent element (Mo, W), x and y are morepreferably in the range of 0<x≦0.5, and 0<y≦0.25, respectively.

The metal-displaced lithium-titanium oxide of the ramsdellite structureexpressed by the formula (1) can be synthesized by a solid phasereaction method. In the solid phase reaction method, Ti source, Lisource and M source are used as starting materials.

While the Ti source includes TiO₂ and titanium compound producing TiO₂by heating (for example, carbonate or nitrate), titanium dioxide (TiO₂)is preferred, and rutile or anatase may be used either alone or incombination. The Li source includes LiO₂ and lithium compound producingLiO₂ by heating (for example, carbonate or nitrate). The M metal sourceincludes M^(V) ₂O₅ and MV compound producing M^(V) ₂O₅ by heating (forexample, carbonate or nitrate of M^(V)), and/or M^(VI)O₃ and M^(VI)compound producing M^(VI)O₃ by heating (for example, carbonate ornitrate of M^(VI)).

These starting materials are mixed by a ratio corresponding to thecomposition ratio of Ti, Li and M in the formula (1), but inconsideration of portion of loss (evaporation) of lithium during baking,a loss is predicted in advance, and the corresponding amount of lithiumis increased accordingly. The adjusted materials are mixed by a ballmill. In mixing process by the ball mill, for example, the rate ofvolume of balls (for example, zirconia balls) to volume of a container(ball volume occupancy) is adjusted to 20%, and balls of about 10 to 15mm in diameter are rotated for 1 hour at a rotating speed of 600 rpm. Inthis case, if the mixing time is too short (less than 30 minutes), theprecursor is not mixed sufficiently, and homogeneous mixed phase ishardly obtained. If the mixing time is too long (more than 2 hours), themechanochemical reaction is progressed too much, and a phase separationmay occur to transform the target compound into a different compound. Inlong-time processing, further, ball components may be mixed with theprecursor.

The mixed material mixture is calcined, and a precursor of the oxideshown by the formula (1) is obtained. The temperature of calcining ispreferably 600 to 800° C. If the calcining temperature is less than 600°C., sufficient mixed state is hardly obtained. If exceeding 800° C.,baking is promoted, and uniform mixing is hardly obtained. The calciningtime is preferably 5 to 20 hours.

The obtained precursor is crushed. The precursor can be crushed by aball mill. In the crushing process by the ball mill, for example, therate of volume of balls (for example, zirconia balls) to volume of acontainer (ball volume occupancy) is adjusted to 20%, and balls of about10 to 15 mm in diameter are rotated for 1 hour at a rotating speed of600 rpm. In this case, if the crushing time is too short (less than 30minutes), the precursor is not crushed sufficiently, and homogeneousmixed phase is hardly obtained. If the crushing time is too long (morethan 2 hours), the mechanochemical reaction is progressed too much, anda phase separation may occur to transform the target compound into adifferent compound. In long-time processing, further, ball componentsmay be mixed with the precursor.

The crushed and mixed precursor is baked. The baking process is executedin atmosphere or in a stream of oxygen gas or nitrogen gas, attemperature of 800 to 1400° C. In this case, in order to obtain adesired ramsdellite structure, it is desired to repeat the operation ofcrushing the baked material again, and baking again in the samecondition, by plural times. The crushing method is not particularlylimited. By compacting the powder by a pressing die or the like and thenbaking, the reactivity can be further enhanced.

If the baking temperature is lower than 800° C., the reactivity is poor,it takes a longer time in baking, and it is hard to obtain a desiredphase. If higher than 1400° C., the evaporation loss amount of lithiumand constituent alkali metal increases, and it is likely to depart fromthe target composition. The total of baking time is approximately 12 to72 hours depending on the baking temperature, and is preferably about 48hours at 900 to 1200° C. The baking atmosphere is preferably air fromthe viewpoint of cost and convenience. However, in the case ofcomposition hard to compose the ramsdellite structure, a desired crystalstructure may be obtained by baking in a nitrogen atmosphere or pureoxygen atmosphere, or by baking at a high pressure.

After completion of baking, it is quenched in order to maintain the hightemperature phase of the ramsdellite structure. Quenching speed may be10° C./sec or more. The quenching medium is atmosphere or liquidnitrogen. From the viewpoint of maintaining the quenching speed, it ispreferred to use a medium of high cooling capability such as liquidnitrogen.

The metal-displaced lithium-titanium oxide of the ramsdellite structureexpressed by the formula (1) can be synthesized also by a sol-gelmethod. In the sol-gel method, titanium alkoxide (for example, titaniumisopropoxide) is used as titanium source, and water-soluble salt (forexample, nitrate) is used as lithium source and metal M source.Specifically, titanium alkoxide is dissolved in ethanol, and an aqueoussolution of water-soluble salt of lithium and water-soluble salt of Mmetal is added while stirring sufficiently by the amounts so that theelements may form the composition as shown in the formula (1), andthereby a gel mixture is obtained. The obtained gel mixture is heated atabout 90 to 120° C., and dried. The obtained powder is baked at 450 to1400° C., and a desired metal-displaced lithium-titanium oxide havingthe ramsdellite structure is obtained. At this time, if the bakingtemperature is lower than 450° C., not only is the reactivity poor, butalso organic components contained in the materials are not decomposedbut are left over in the structure. If the baking temperature is higherthan 1400° C., part of components may be lost by evaporation, and it islikely to depart from the target composition.

The obtained metal-displaced lithium-titanium oxide expressed by theformula (1) is preferably used in a nonaqueous electrolyte battery,especially as a negative electrode active material of a nonaqueouselectrolyte lithium secondary battery. This oxide causesoxidation-reduction reaction between Ti³⁺ and Ti⁴⁺ when intercalatingand deintercalating lithium, and a potential plateau of about 1.2 to1.6V occurs in metal lithium electrochemically. Further, by theoxidation-reduction potential of displaced elements of higher valency, asecond stage of potential plateau occurs. By intercalating anddeintercalating lithium ions, the material can be used as a negativeelectrode active material of a lithium battery. As the negativeelectrode active material, the metal-displaced lithium-titanium oxideexpressed by the formula (1) may be used alone, or this oxide may becombined with other known negative electrode active material, forexample, spinel type lithium titanate (e.g. Li_(4+x)Ti₅O₁₂ (x being−1≦x≦3), or titanium oxide (e.g. TiO₂ or metal composite oxidecontaining at least one element selected from the group consisting ofTi, P, V, Sn, Cu, Ni and Fe, TiO₂—P₂O₅, TiO₂—V₂O₅, TiO₂—P₂O₅—SnO₂). Whenused in combination with other known negative electrode active material,the metal-displaced lithium-titanium oxide expressed by the formula (1)is preferred to occupy 50 wt % or more of the total negative electrodeactive material.

The average particle size of the negative electrode active material isdesirably 1 μm or less. By using the negative electrode active materialhaving average particle size of 1 μm or less, the cycle performance of anonaqueous electrolyte secondary battery can be enhanced. Especially,this effect is outstanding at the time of charging at high speed ordischarging at high output. However, if the average particle size is toosmall, distribution of nonaqueous electrolyte may be biased to thenegative electrode side, and the electrolyte may be depleted in thepositive electrode. Therefore, the lower limit of the particle size isdesired to be 0.001 μm. The negative electrode active material havingsuch average particle size is obtained by crushing the negativeelectrode active material by a ball mill until the average particle sizebecomes 1 μm or less. In crushing process by the ball mill, for example,the ratio of volume of balls (for example, zirconia balls) to volume ofa container (ball volume occupancy) is adjusted to 20%, large balls ofabout 10 to 15 mm in diameter and small balls of about 5 mm in diameterare used, and the ball mill is rotated at a rotating speed of 600 rpm.In this case, crushing is not executed continuously, but is preferablyexecuted intermittently at specific intervals. This is intended to avoiddegeneration of active material caused by friction heat by mixing.

The average particle size of the negative electrode active material ismeasured by using a laser diffraction type distribution measuringinstrument (SALD-300 of Shimadzu Corporation). First, about 0.1 g ofactive material sample, surface active agent, and 1 to 2 mL of distilledwater are added in a beaker, and stirred and mixed sufficiently. Thismixed solution is then poured into an agitating water tank, and whilebeing agitated, the luminous intensity distribution is measured a totalof 64 times at intervals of 2 seconds to numerically analyze theparticle size distribution, thereby determining the average particlesize of the negative electrode active material.

<Negative Electrode>

The negative electrode of the invention includes a conductive basematerial (negative electrode current collector) and a negative electrodeactive layer formed on the surface of the conductive base material (oneor both of two principal planes). The negative electrode active layer isa layer responsible for negative electrode reaction, that is, a layeractive as negative electrode, and contains the negative electrode activematerial of the invention.

The negative electrode active layer contains a conductive agent inaddition to the negative electrode active material of the invention, andusually contains a binder for binding them. Examples of the conductiveagent include acetylene black, ketjen black, graphite, and other metalpowder. Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), fluororubber, and styrene butadienerubber.

The blending ratio of the negative electrode active material, conductiveagent, and binder is preferably in the range of 80 to 98 mass % ofnegative electrode active material, 0 to 20 mass % of conductive agent,and 2 to 7 mass % of binder.

The negative electrode current collector is desired to be formed of aconductive material, such as aluminum foil or aluminum alloy foil. Thenegative electrode current collector is desired to be 50 μm or less inaverage crystal particle size. As a result, the strength of the currentcollector is increased remarkably, and the negative electrode can becompacted to high density at high pressure, thereby increasing thebattery capacity. It is also effective to prevent dissolution, corrosionor deterioration of the negative electrode current collector inoverdischarging cycles in a high temperature environment (over 40° C.),and thus elevation of negative electrode impedance can be suppressed.Further, output characteristics, fast charge, and charging anddischarging cycle characteristics can be improved. A more desirablerange of the average crystal particle size is 30 μm or less, furtherpreferably 5 μm or less.

The average crystal particle size of the negative electrode currentcollector can be determined as follows. The texture of the negativeelectrode current collector surface is observed by an opticalmicroscope, and the number n of crystal grains existing in an area of 1mm×1 mm is counted. By using the value of n, an average crystal particlearea S is determined by the formula S=1×10⁶/n (μm²). From the obtainedvalue of S, an average crystal particle size d (μm) is calculated by theformula (A):d=2(S/π)^(1/2)  (A)

The average crystal particle size of aluminum foil and aluminum alloyfoil varies due to effects of various factors, such as material texture,impurities, processing condition, history of heat treatment, andannealing condition. The crystal particle size can be adjusted bycombining these factors in the manufacturing process of the currentcollector.

The thickness of aluminum foil and aluminum alloy foil is usually 20 μmor less, preferably 15 μm or less. The purity of aluminum foil isdesired to be 99 mass % or more. An aluminum alloy is an alloypreferably containing magnesium, zinc or silicon. The content oftransition metal such as iron, copper, nickel or chromium is desired tobe 1 mass % or less.

The negative electrode can be manufactured by adding a binder and, ifnecessary, conductive agent to the negative electrode active material ofthe invention, suspending them in a proper solvent, and applying thesuspension to the negative electrode current collector (conductive basematerial), followed by drying and pressing.

<Nonaqueous Electrolyte Battery>

The nonaqueous electrolyte battery of the invention includes a negativeelectrode, a positive electrode, and a nonaqueous electrolyte providedbetween the negative electrode and the positive electrode, and thenegative electrode is configured as explained above.

The positive electrode includes a conductive base material (positiveelectrode current collector) and a positive electrode active layerformed on one or both sides of the current collector. The positiveelectrode current collector includes a positive electrode activematerial, and a conductive agent as required, and a binder for bindingthem.

Examples of the positive electrode active material include various metaloxides and sulfides. The examples include manganese dioxide (MnO₂), ironoxide, copper oxide, nickel oxide, lithium-manganese composite oxide(e.g. Li_(x)Mn₂O₄ or Li_(x)M_(n)O₂), lithium-nickel composite oxide(e.g. Li_(x)NiO₂), lithium-cobalt composite oxide (Li_(x)CoO₂),lithium-nickel-cobalt composite oxide {e.g. LiNi_(1-y-z)Co_(y)M₂O₂ (Mbeing at least one element selected from the group consisting of Al, Crand Fe), 0≦y≦0.5, 0≦z≦0.1}, lithium-manganese-cobalt composite oxide{e.g. LiMn_(1-y-z)Co_(y)M_(z)O₂ (M being at least one element selectedfrom the group consisting of Al, Cr and Fe), 0≦y≦0.5, 0≦z≦0.1},lithium-manganese-nickel composite oxide {e.g. LiMn_(x)Ni_(x)M_(1-2x)O₂(M being at least one element selected from the group consisting of Co,Cr, Al, and Fe), ⅓≦x≦½, e.g. LiMn_(1/3)Ni_(1/3)Co_(1/3)O₂,LiMn_(1/2)Ni_(1/2)O₂}, spinel type lithium-manganese-nickel compositeoxide (LixMn_(2-y)Ni_(y)O₄), lithium-phosphorus oxide having an olivinestructure (Li_(x)FePO₄, Li_(x)Fe_(1-y)Mn_(y)PO₄, Li_(x)CoPO₄, etc.),iron sulfate {Fe₂(SO₄)₃}, and vanadium oxide (e.g. V₂O₅). Other examplesinclude conductive polymer materials such as polyaniline andpolypyrrole, disulfide polymer, sulfur (S), carbon fluoride, otherorganic materials and inorganic materials. The values of x, y and z aredesired to be in the range of 0 or more to 1 or less.

More preferred examples of the positive electrode active material for asecondary battery include lithium-manganese composite oxide,lithium-nickel composite oxide, lithium-cobalt composite oxide,lithium-nickel-cobalt composite oxide, lithium-manganese-nickelcomposite oxide, spinel type lithium-manganese-nickel composite oxide,lithium-manganese-cobalt composite oxide, and lithium ion phosphate. Byusing these positive electrode active materials, a high battery voltageis obtained.

The conductive agent and binder may be the same as those used in thenegative electrode.

The blending ratio of the positive electrode active material, conductiveagent, and binder is preferably in the range of 80 to 95 mass % ofpositive electrode active material, 3 to 20 mass % of conductive agent,and 2 to 7 mass % of binder.

The positive electrode current collector can be formed by using the sameconductive material as used in the negative electrode current collector.

The positive electrode is manufactured in the same procedure as inmanufacture of the negative electrode.

The nonaqueous electrolyte provided between the negative electrode andthe positive electrode contains nonaqueous solvent, and electrolyticsalt dissolved in this nonaqueous solvent. The nonaqueous solvent maycontain polymer.

Examples of the nonaqueous solvent are not particularly limited, but mayinclude, among others, propylene carbonate (PC), ethylene carbonate(EC), 1,2-dimethoxy ethane (DME), γ-butyrolactone (GBL), tetrahydrofuran(THF), 2-methyl tetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane,acetonitrile (AN), diethyl carbonate (DEC), dimethyl carbonate (DMC),methyl ethyl carbonate (MEC), and dipropyl carbonate (DPC). Thesesolvents may be used either alone or in combination of two or moretypes. In particular, γ-butyrolactone is preferred. When two or moresolvents are combined, it is preferred to select solvents havingdielectric constant of 20 or more.

Examples of the electrolytic salt include lithium salts such as LiPF₆,LiBF₄, Li (CF₃SO₂)₂N (bistrifluoromethane sulfonylamide lithium; knownas LiTFSI), LiCF₃SO₃ (known as LiTFS), Li(C₂F₄SO₂)₂N (bispentanefluoroethane sulfonylamide lithium; known as LiBETI), LiClO₄, LiAsF₆,LiSbF₆, bisoxolate lithium phosphate (LiB (C₂O₄)₂ (known as LiBOB)), anddifluoro (trifluoro-2-oxide-2-trifluoro-methyl propionate (2-)-0,0)lithium phosphate (LiBF₂(OCOOC(CF₃)₂ (known as LiBF₂ (HHIB))). Theseelectrolytic salts may be used either alone or in combination of two ormore types. In particular, LiPG₆ and LiBF₄ are desirable.

The concentration of electrolytic salt is desirably in the range of 1.5Mor more to 3M or less.

Additives may be added to the nonaqueous electrolyte. Examples of theadditives are not particularly limited, and may include vinylenecarbonate (VC), vinylene acetate (VA), vinylene butylate, vinylenehexanate, vinylene crotonate, and catechol carbonate. The concentrationof the additive is preferably 0.1 mass % or more to 3 mass % or lesswith respect to 100 mass % of nonaqueous electrolyte. A more desirablerange is 0.5 wt % or more to 1 wt % or less.

Between the negative electrode and the positive electrode, a separatoris usually disposed for preventing contact between the negativeelectrode and the positive electrode, and for keeping a space forholding the nonaqueous electrolyte.

The material of the separator includes polyethylene, polypropylene,cellulose, polyvinylidene fluoride (PVdF), other porous film, andsynthetic resin unwoven cloth. In particular, a porous film made ofpolyethylene or polypropylene is dissolved by abnormal exothermicreaction to close pores, thereby shutting off conduction between thenegative electrode and the positive electrode, and is hence preferredfrom the viewpoint of enhancement of safety.

Such nonaqueous electrolyte lithium secondary battery is excellent inrepeated charging and discharging performance, high in capacity density,and is also excellent in rapid charging and discharging performance.

First Embodiment

Referring now to FIGS. 2 to 6, a nonaqueous electrolyte batteryaccording to a first embodiment of the invention will be describedbelow.

As shown in FIG. 2, a flat spirally wound coiled type electrode group 16is housed in an armoring member 17. The coiled type electrode group 16includes a positive electrode 13, a negative electrode 14, and aseparator 15 interposed therebetween (FIG. 3), being spirally wound in aflat shape. The nonaqueous electrolyte is held in the coiled electrodegroup 16.

As shown in FIG. 3, the negative electrode 14 is positioned on theoutermost circumference of the coiled electrode group 16. At the innercircumferential side of the negative electrode 14, the separator 15,positive electrode 13, separator 15, negative electrode 14, separator15, positive electrode 13, and separator 15 are disposed in this order.The negative electrode 14 includes a negative electrode currentcollector 14 a, and a negative electrode active material containinglayer 14 b carried on the negative electrode current collector 14 a. Inthe portion positioned on the outermost circumference of the negativeelectrode 14, the negative electrode active material containing layer 14b is formed only on one side of the negative electrode current collector14 a. The positive electrode 13 includes a positive electrode currentcollector 13 a, and a positive electrode active material containinglayer 13 b carried on the positive electrode current collector 13 a.

As shown in FIG. 2, a positive electrode terminal 11 is electricallyconnected to the positive electrode current collector 13 a near theouter circumferential end of the coiled electrode group 16. On the otherhand, a negative electrode terminal 12 is electrically connected to thenegative electrode current collector 14 a near the outer circumferentialend of the coiled electrode group 16. The shape of the positiveelectrode terminal 11 and the negative electrode terminal 12 is like aband. The leading ends of these terminals 11, 12 are drawn to theoutside from the same side of the armoring member 17.

In this embodiment, the electrode group is in a coiled structure, butthe electrode group may be also formed in a laminate structure as shownin FIGS. 4 and 5. A laminate type electrode group 19 is surrounded by anarmoring member 18 made of a laminate film. The laminate film 18includes, as shown in FIG. 4, a resin layer 20, a thermofusible resinlayer 21, and a metal layer 22 interposed between the resin layer 20 andthe thermofusible resin layer 21. At the inner side of the armoringmember 18, the thermofusible resin layer 21 is positioned. At one longerside and both shorter sides of the armoring member 18, heat seals 18 a,18 b, 18 c are formed by thermal fusion of the thermofusible resin layer21. The armoring member 18 is sealed by these heat seals 18 a, 18 b, 18c.

The laminate type electrode group 19 includes a plurality of positiveelectrodes 13, a plurality of negative electrode 14, and separators 15interposed between the positive electrodes 13 and the negativeelectrodes 14. The laminate type electrode group 19 has a structure asshown in FIG. 5, in which the positive electrodes 13 and the negativeelectrodes 14 are laminated alternately together while interposing theseparators 15 therebetween. Each of the positive electrodes 13 includesa positive electrode current collector 13 a, and a positive electrodeactive material containing layer 13 b carried on both sides of thepositive electrode current collector 13 a. Each of the negativeelectrodes 14 includes a negative electrode current collector 14 a, anda negative electrode active material containing layer 14 b carried onboth sides of the negative electrode current collector 14 a. Thenegative electrode current collector 14 a of the negative electrode 14has one short side projected from the positive electrode 13. Thenegative electrode current collector 14 a projecting from the positiveelectrode 13 is electrically connected to the band-like negativeelectrode terminal 12. The leading end of the negative electrodeterminal 12 is drawn to the outside through the heat seal 18 c of thearmoring member 18. The heat seals 18 c at both sides of the negativeelectrode terminal 12 are opposite to a pair of thermofusible resinlayers 21 respectively by way of an insulating film 23. To enhance thebonding strength of the heat seal 18 c and the negative electrodeterminal 12, the insulating film 23 is interposed between each side ofthe negative electrode terminal 12 and the thermofusible resin layer 21.The insulating film 23 is, for example, a film formed by adding an acidanhydride to polyolefin containing at least one of polypropylene andpolyethylene.

Although not shown in the drawing, the positive electrode currentcollector 13 a of the positive electrode 13 has its one short sideprojecting from the negative electrode 14. The projecting direction ofthe positive electrode current collector 13 a is opposite to theprojecting direction of the negative electrode current collector 14 a.The positive electrode current collector 13 a projecting from thenegative electrode 14 is connected electrically to the band-likepositive electrode terminal 11. The leading end of the positiveelectrode terminal 11 is drawn to the outside through the heat seal 18 bof the armoring member 18. To enhance the bonding strength of the heatseal 18 b and the positive electrode terminal 11, the insulating film 23is interposed between the positive electrode terminal 11 and thethermofusible resin layer 21. The withdrawing direction of the positiveterminal 11 from the armoring member 18 is opposite to the withdrawingdirection of the negative terminal 12 from the armoring member 18.

To realize a high large-current performance during operation for a longtime, the electrode group including positive electrodes and negativeelectrodes is preferred to be in a laminate structure, with theseparator folded in a zigzag pattern as shown in FIG. 6. The band-likeseparator 15 is folded in a zigzag pattern. Between the zigzag-foldedseparators 15, strips of positive electrode 13 c, negative electrode 14c, positive electrode 13 d, and negative electrode 14 d are sequentiallyinserted from above. From the shorter sides of the positive electrodes13 c, 13 d, positive electrode terminals 24 are drawn out. By disposingthe positive electrodes 13 and the negative electrodes 14 alternatelybetween the zigzag-folded separators 15, an electrode group of alaminate structure is obtained.

The armoring member, the negative electrode terminal and the positiveelectrode terminal will be specifically described below.

The armoring member is, for example, a laminate film having thickness of0.2 mm or less, or a metal container having a wall thickness of 0.5 mmor less. The wall thickness of a metal container is more preferably 0.2mm or less.

The laminate film is a multilayer film consisting of a metal layer and aresin layer for covering the metal layer. For reduction of weight, themetal layer is preferably an aluminum foil or an aluminum alloy foil.The resin layer is to reinforce the metal layer, and is made of highpolymer such as polypropylene (PP), polyethylene (PE), nylon, orpolyethylene terephthalate (PET). The laminate film is formed by sealingby thermal fusion.

The metal container is made of, for example, aluminum or aluminum alloy.An aluminum alloy is preferably an alloy containing an element such asmagnesium, zinc or silicon. The content of transition metal, such asiron, copper, nickel, or chromium is preferably 1% or less. As a result,the long-term reliability and heat release performance in a hightemperature environment can be enhanced outstandingly.

The metal container formed of aluminum or aluminum alloy is preferred tobe 50 μm or less in average crystal particle size, more preferably 30 μmor less, and further preferably 5 μm or less. By defining the averagecrystal particle size at 50 μm or less, the strength of the metalcontainer formed of aluminum or aluminum alloy is increasedoutstandingly, and the wall thickness can be further reduced. As aresult, a battery of light weight, high output, and excellent long-termreliability, and being suited to be mounted on a vehicle is realized.

The nonaqueous electrolyte battery of the invention is not limited tothe one using the above-described container made of a laminate film, andfor example, a metal container as shown in FIG. 7 can be used.

The armoring member includes a battery container 81 made of aluminum oraluminum alloy for forming a bottomed square tubular form, a lid 82disposed at the opening of the container 81, and a negative electrodeterminal 84 attached to the lid 82 by way of an insulator 83. Thecontainer 81 serves also as a positive electrode terminal. The aluminumor aluminum alloy for composing the container 81 may be a materialhaving the composition and average crystal particle size as mentionedabove.

The electrode group 85 is housed in the battery container 81. Theelectrode group 85 is formed in a structure having positive electrodes86 and negative electrodes 87 wound in a flat shape by way ofinterposing separators 88. The electrode group 85 is, for example,obtained by laminating the positive electrode 86, separator 88, andnegative electrode 87 in this order to form a band-like structure, andcoiling and winding by using a plate or cylindrical core so that thepositive electrode 86 may be located at the outer side, followed bypressuring and forming the obtained coil in the radial direction.

The nonaqueous electrolyte solution (liquid nonaqueous electrolyte) isheld in the electrode group 85. A spacer 90 composed of, for example,synthetic resin having a lead take-out hole 89 nearly in the center isdisposed on the electrode group 85 in the container 81.

Near the center of the lid 82, a take-out hole 91 of the negativeelectrode terminal 84 is opened. A liquid injection port 92 is providedat a position apart from the take-out hole 91 of the lid 82. The liquidinjection port 92 is sealed by a sealing plug 93 after injecting thenonaqueous electrolyte solution into the container 81. The negativeelectrode terminal 84 is hermetically sealed in the take-out hole 91 ofthe lid 82 by way of the insulator 83 made of glass or resin.

A negative electrode lead tab 94 is welded at the lower end of thenegative electrode terminal 84. The negative electrode lead tab 94 iselectrically connected to the negative electrode 87. One end of apositive electrode lead 95 is electrically connected to the positiveelectrode 86, and other end thereof is welded to the lower side of thelid 82. An insulating paper 96 covers the entire outer surface of thelid 82. An armoring tube 97 covers the entire side surface of thecontainer 81, and upper and lower ends are folded to the upper and lowersides of the battery main body.

The battery container is not limited to the shape of square tube, butmay be formed in other shapes, such as flat shape, cylindrical shape,coin shape, button shape, sheet shape or laminate shape. In addition toa small-sized battery to be used in portable electronic appliances, itmay be formed as a large-sized battery to be mounted on a two-wheel orfour-wheel automobile or the like.

The negative electrode terminal can be formed of a material havingelectrical stability and conductivity in the range of potential tolithium ion metal from 0.4V or more to 3V or less. Specific examples arealuminum or aluminum alloy containing any element selected from Mg, Ti,Zn, Mn, Fe, Cu, and Si. Preferably, it is made of the same material asthe negative electrode current collector in order to decrease thecontact resistance.

The positive electrode terminal can be formed of a material havingelectrical stability and conductivity in the range of potential tolithium ion metal from 3V or more to 5V or less. Specific examples arealuminum or aluminum alloy containing any element selected from Mg, Ti,Zn, Mn, Fe, Cu, and Si. Preferably, it is made of the same material asthe positive electrode current collector in order to decrease thecontact resistance.

Second Embodiment

Referring now to FIG. 8, a battery pack according to a second embodimentwill be explained.

The battery pack of the second embodiment has a plurality of nonaqueouselectrolyte batteries of the first embodiment as single batteries. Theindividual single batteries are electrically arrayed in series or inparallel to form a battery module. Examples of the single batteriesinclude batteries in the types as shown in FIG. 2, 4, or 7.

As mentioned above, the single batteries of the first embodiment areexcellent in repeated charging and discharging performance, high incapacity density, and also excellent in rapid charging and dischargingperformance. When a battery pack is formed by using such singlebatteries, the entire structure is reduced in size if the designspecification is the same as in the performance of a conventionalproduct.

As shown in FIG. 8, single batteries 121 for composing a battery pack 54are flat nonaqueous electrolyte batteries shown in FIG. 2. The pluralityof single batteries 121 are laminated in the battery thicknessdirection, and the side surface from which a positive electrode terminal101 and a negative electrode terminal 102 are projected is opposite to aprinted wiring board 124 individually. These single batteries 121 areconnected in series to compose one battery module 122. The batterymodule 122 is integrally bundled by an adhesive tape 123.

The printed wiring board 124 is disposed at the side surface from whichthe positive electrode terminal 101 and the negative electrode terminal102 are projected. A thermistor 125, a protective circuit 126, and aterminal 127 for feeding power to an external device (FIG. 9) aremounted on the printed wiring board 124.

As shown in FIGS. 9 and 8, a positive electrode side wiring 128 of thebattery module 122 is electrically connected to a positive electrodeside connector 129 of the protective circuit 126 of the printed wiringboard 124. A negative electrode side wiring 130 of the battery module122 is electrically connected to a negative electrode side connector 131of the protective circuit 126 of the printed wiring board 124.

The thermistor 125 is for detecting the temperature of the singlebatteries 121, and the detected signal is sent to the protective circuit126. The protective circuit 126 can shut off a plus side wiring 131 aand a minus side wiring 131 b between power feed terminals of theprotective circuit and external device in a specified condition. Thespecified condition is, for example, when the temperature detected bythe thermistor exceeds a predetermined temperature, or whenovercharging, overdischarging or overcurrent of the single batteries 121is detected. The condition is detected in the individual singlebatteries 121 or in the entire single batteries 121. When detecting theindividual single batteries 121, the battery voltage may be detected, orthe positive electrode voltage or negative electrode voltage may bedetected. In the latter case, a lithium electrode is inserted in theindividual single batteries 121 as a reference electrode. In the circuitshown in FIG. 9, a wiring 132 for detecting voltage is connected to eachsingle battery 121, and the detection signal is sent to the protectivecircuit 26 through the wiring 132.

In the battery module 122, protective sheets 133 of rubber or resin aredisposed on three side surfaces other than the side surface from whichthe positive electrode terminal 101 and the negative electrode terminal102 are projected. A protective block 134 of rubber or resin is disposedbetween the printed wiring board 124 and the side surface from which thepositive electrode terminal 101 and the negative electrode terminal 102are projected.

This battery module 122 is housed in a pack container 135 together withthe protective sheets 133, the protective block 134, and the printedwiring board 124. That is, the protective sheets 133 are disposed atboth inner sides in the longer side direction and an inner side in theshorter side direction of the pack container 135, and the printed wiringboard 124 is disposed at the opposite inner side of the shorter sidedirection. The battery module 122 is positioned in the space surroundedby the protective sheets 133 and the printed wiring board 124. A lid 136is provided on the top of the pack container 135.

To fix the battery module 122, instead of the adhesive tape 123, aheat-shrink tube may be used. In this case, the protective sheets areplaced at both sides of the battery module, the heat-shrink tube is thenwound around the battery module, and the heat-shrink tube is shrunk byheat to bundle the battery module tightly.

In FIGS. 8 and 9, the single batteries 121 are connected in series, butthey may be connected in parallel to increase the battery capacity. Theassembled battery packs 54 may be connected either in series or inparallel.

The aspect of the battery pack may be changed properly according to theapplication.

The battery pack of the second embodiment is expected to be applied inlarge current cycle performance. Specific examples are power source ofdigital camera, two-wheel or four-wheel hybrid car, two-wheel orfour-wheel electric vehicle, and power-assisted bicycle. In particular,a car-mount use is preferred.

When the nonaqueous electrolyte contains at least one of propylenecarbonate (PC) and ethylene carbonate (EC), and γ-butyrolactone (GBL),applications of high temperature performance are desirable. Specificexamples are the above-described car-mount applications.

Third Embodiment

Referring to FIGS. 10 to 15, a vehicle and a motorbike according to athird embodiment will be explained.

The vehicle of the third embodiment has the battery pack 54 of thesecond embodiment. As mentioned above, the battery pack 54 of the secondembodiment is excellent in repeated charging and dischargingperformance, high in capacity density, and excellent in rapid chargingand discharging performance, and is generally reduced in size ifdesigned in the same specification as in the performance of aconventional product. By using such battery pack 54, the power sourcesystem of the vehicle can be reduced in size. The vehicle mentioned hereincludes a two-wheel or four-wheel hybrid electric vehicle, a two-wheelor four-wheel electric vehicle, and a power-assisted bicycle.

FIGS. 10 to 12 show the hybrid vehicle combining an internal combustionengine and a battery-driven motor as the driving power source. Fordriving a vehicle, a driving source having a wide range of rotatingspeed and torque is needed depending on the running condition.Generally, the internal combustion engine is limited in the torque androtating speed showing an ideal energy efficiency, and is lowered in theenergy efficiency in other operating conditions. In a hybrid typevehicle, while operating the internal combustion engine in an optimumcondition to generate power, the wheels are driven by a motor of highefficiency, or the power outputs of the internal combustion engine andmotor are combined, thereby improving the energy efficiency of theentire vehicle. When decelerating, the kinetic energy of the vehicle isregenerated as electric power, and the running distance per unit fuelconsumption can be extended dramatically as compared with theconventional vehicle driven by the internal combustion engine alone.

Hybrid vehicles can be roughly classified into three categoriesdepending on the combination of an internal combustion engine and anelectric motor.

FIG. 10 shows a hybrid vehicle 50 generally known as series hybridvehicle. The power of the internal combustion engine 51 is onceconverted totally into an electric power by a generator 52, and thiselectric power is stored in the battery pack 54 through an inverter 53.The battery pack 54 is the battery pack according to the secondembodiment of the invention. The electric power of the battery pack 54is supplied to a motor 55 through the inverter 53, and wheels 56 aredriven by the motor 55. This is a combined system of the electricvehicle and the generator 52. The internal combustion engine 51 can beoperated in a condition of high efficiency, and can regenerate theelectric power. To the contrary, since the wheels 56 are driven by themotor 55 only, the motor 55 of high output is needed. The battery pack54 is also required to be relatively large in capacity. The ratedcapacity of the battery pack 54 is desired to be in the range of 5 to 50Ah. A more desirable range is 10 to 20 Ah. Herein, the rated capacity isthe capacity when the battery is discharged at a rate of 0.2 C.

FIG. 11 shows a hybrid vehicle 57 generally known as parallel hybridvehicle. Reference numeral 58 is a motor functioning also as agenerator. The internal combustion engine 51 mainly drives the wheels56, part of its power is converted as required into an electric power bythe generator 58, and the battery pack 54 is charged by this electricpower. The driving power is assisted by the motor 58 when the vehiclestarts with a heavy load or at the time of acceleration. This system isbased on an ordinary vehicle. In this system, a high efficiency isachieved by suppressing load fluctuations of the internal combustionengine 51, and the electric power is also regenerated. Since the wheels56 are mainly driven by the internal combustion engine 51, the output ofthe motor 58 can be determined arbitrarily depending on the rate of thenecessary assistance. The system can be built by using a relativelysmall motor 58 and battery pack 54. The rated capacity of the batterypack 54 is desirably in the range of 1 to 20 Ah. A more desirable rangeis 3 to 10 Ah.

FIG. 12 shows a hybrid vehicle 59 generally known as series-parallelhybrid vehicle. This is a combination of series type and parallel type.A power separation mechanism 60 separates the output of the internalcombustion engine 51 into power generation use and wheel driving use.The engine load can be controlled more delicately than in the parallelsystem, and the energy efficiency can be enhanced.

The rated capacity of the battery pack is desirably in the range of 1 to20 Ah. A more desirable range is 3 to 10 Ah.

The nominal voltage of the battery pack 54 mounted on the hybridvehicles shown in FIGS. 10 to 12 is desirably in the range of 200 to600V.

The battery pack 54 is generally desired to be installed in a placewhich is hardly subject to changes in ambient temperature, and is notexposed to impact of collision or the like. For example, in the case ofa sedan type vehicle as shown in FIG. 13, the battery pack is installedin a trunk room 62 behind rear seats 61. It can be also disposed in thelower part or rear part of the seats 61. In the case of a heavy battery,it is desired to be disposed beneath the seats or beneath the floor inorder to lower the center of gravity of the entire vehicle.

An electric vehicle (EV) is driven by the energy stored in the batterypack 54 being charged by an electric power supplied from outside of thevehicle. Therefore, the electric vehicle can utilize the electric energygenerated efficiently by other power generation facility. Whendecelerating, since the kinetic energy of the vehicle can be regeneratedas electric power, the energy efficiency in running operation can beenhanced. Since the electric vehicle emits no carbon dioxide or otherexhaust gas, it is a clean vehicle. On the other hand, since all drivingpower depends on the motor, a motor of high output is needed. Generally,since all energy necessary for one cruise must be stored in the batterypack 54 before running by one charging operation, a battery of a verylarge capacity is needed. The rated capacity of the battery pack 54 isdesirably in the range of 100 to 500 Ah. A more desirable range is 200to 400 Ah.

Further, since the rate of battery weight occupied in the vehicle weightis high, the battery pack 54 is preferably laid down beneath the flooror disposed at a lower position, not largely apart from the center ofgravity of the vehicle. To charge a large energy consumed by one cruisein a short time, a charger and a charging cable of large capacity arenecessary. Accordingly, the electric vehicle is desired to be providedwith a charging connector for connecting them. The charging connectormay be either an ordinary connector by electric contact, or acontactless charging connector by electromagnetic coupling.

FIG. 14 shows an example of a hybrid motorbike 63. In the case of atwo-wheel vehicle, as in the hybrid vehicle, a hybrid motorbike of highenergy efficiency can be constructed by including an internal combustionengine 64, a motor 65, and a battery pack 54. The internal combustionengine 64 mainly drives the wheel 66, and part of its power is used forcharging the battery pack 54 if necessary. When the load is heavy uponstart-up or acceleration, the driving force is assisted by the motor 65.Since the wheel 66 is mainly driven by the internal combustion engine64, the output of the motor 65 can be determined arbitrarily dependingon the rate of the necessary assistance. The system can be built byusing a relatively small motor 65 and battery pack 54. The ratedcapacity of the battery pack 54 is desirably in the range of 1 to 20 Ah.A more desirable range is 3 to 10 Ah.

FIG. 15 shows an example of an electric motorbike 67. The electricmotorbike 67 is driven by the energy stored in the battery pack 54 beingcharged by an electric power supplied from outside. Since all drivingpower depends on the motor 65, the motor 65 needs to have high output.Generally, since all energy necessary for one cruise must be stored inthe battery pack before running by one charging operation, a battery ofa relatively large capacity is needed. The rated capacity of the batterypack 54 is desirably in the range of 10 to 50 Ah. A more desirable rangeis 15 to 30 Ah.

As mentioned above, the battery pack 54 of the second embodiment isexcellent in repeated charging and discharging performance, high incapacity density, and excellent in rapid charging and dischargingperformance, and is generally reduced in size if designed in the samespecification as in the performance of a conventional product. By usingsuch battery pack 54, the power source system of an electric motorbikecan be reduced in size.

Fourth Embodiment

A rechargeable vacuum cleaner according to a fourth embodiment will beexplained by referring to FIGS. 16 and 17. A rechargeable vacuum cleaner70 includes an operation unit 75 for selecting operation modes, anelectric blower 74 composed of a fan motor or the like for creating asuction force for collecting dust, and a control circuit 73. As thepower source for driving these parts, the battery pack 54 of the secondembodiment is housed in a casing 72 of the vacuum cleaner. Whenincorporating the battery pack 54 in such a portable device, it isdesired to fix the battery pack 54 by using a buffer material forsuppressing the effects of vibration or impact. To maintain the batterypack 54 at an appropriate temperature, a known temperature controltechnology can be applied. Part or whole of the charger function of acharger 71, used also as a cradle, may be housed in the casing 72.

The power consumption of the rechargeable vacuum cleaner 70 is large,but considering the portability and continuous operating time, the ratedcapacity of the battery pack 54 is desirably in the range of 2 to 10 Ah.A more desirable range is 2 to 4 Ah. The nominal voltage of the batterypack 54 is desirably in the range of 40 to 80V.

As mentioned above, the battery pack 54 of the second embodiment isexcellent in repeated charging and discharging performance, high incapacity density, and excellent in rapid charging and dischargingperformance, and is generally reduced in size if designed in the samespecification as in the performance of a conventional product. By usingsuch battery pack 54, the power source system of the rechargeable vacuumcleaner 70 can be reduced in size.

EXAMPLES

The invention will be more specifically described below by showingvarious examples, but the invention is not limited to these examplesalone. The crystal phase obtained by reaction was identified by a powderX-ray diffraction method.

In Examples 1 to 4, ramsdellite compounds whose Ti sites were displacedwith Ta, Mo, W, and Nb were synthesized, and the charging anddischarging behavior, and Li ion conductivity were investigated bymeasuring the AC impedance. In Comparative Example 1, a knownramsdellite compound Li₂Ti₃O₇ was used, and in Comparative Example 2,titanium oxide compounds, in which Sn having the same valency as Ti wasused as a substituent element M, were synthesized to investigate thecharging and discharging behavior and Li ion conductivity.

Examples 1 and 2

In Examples 1 and 2, metal-displaced lithium-titanium oxides of aramsdellite type structure expressed by the formula (1) in which MV isTa (example 1) or M^(V) is Nb (example 2) were synthesized.

Materials were lithium carbonate (Li₂CO₃), titanium dioxide (TiO₂), andtantalum pentoxide (Ta₂O₅) or niobium pentoxide (Nb₂O₄), which wereblended at an element ratio Li:Ti:M^(V) of 1.9:2.9:0.1, that is, x=0.1,y=0.1, and mixed for 1 hour in a ball mill. At this time, by addinglithium carbonate about 5% more than the element ratio, the loss bybaking process was compensated. In a muffle electric furnace, thematerials were calcined in atmosphere, for 2 hours at 650° C., and for12 hours at 800° C. The obtained mixed powder was mixed again in a ballmill for 1 hour, baked for 12 hours at 1100° C., and pulverized again.The obtained powder was compacted by a uniaxial pressure moldingmachine, and pelletized. The obtained pellets were similarly baked for36 hours at 1100° C. To obtain a ramsdellite structure reliably, thepellets were quenched from the baking temperature to room temperature.In the quenching process, the temperature was quickly lowered to lessthan room temperature by using liquid nitrogen.

FIG. 18 shows a powder X-ray diffraction pattern of obtained titaniumoxide compound baked powder. In the diagram, the peak corresponding tothe ramsdellite type crystal structure is indicated by an invertedtriangle mark. As is clear from the diagram, almost all the peaks arederived from the ramsdellite type crystal structure, and can beexponentiated. The oxides of Examples 1 and 2 were found to show asingle phase of the ramsdellite type crystal structure.

Examples 3 and 4

In Examples 3 and 4, metal-displaced lithium-titanium oxides of aramsdellite type structure expressed by the formula (1) in which M^(VI)is Mo (example 3) or M^(VI) is W (example 4) were synthesized.

Materials were lithium carbonate (Li₂CO₃), titanium dioxide (TiO₂), andmolybdenum trioxide (MoO₃) or tungsten trioxide (WO₃), which wereblended at an element ratio Li:Ti:M^(VI) of 1.8:2.9:0.1, that is, x=0.2,y=0.1, and mixed for 1 hour in a ball mill. At this time, by addinglithium carbonate about 5% more than the element ratio, the loss bybaking process was compensated. In a muffle electric furnace, thematerials were calcined in atmosphere, for 2 hours at 650° C., and for12 hours at 800° C. The obtained mixed powder was mixed again in a ballmill for 1 hour, baked for 12 hours at 1100° C., and pulverized again.The obtained powder was compacted by a uniaxial pressure moldingmachine, and pelletized. The obtained pellets were similarly baked for36 hours at 1100° C. To obtain a ramsdellite structure reliably, thepellets were quenched from the baking temperature to room temperature.In the quenching process, the liquid nitrogen was used as in Examples 1and 2.

From the powder X-ray diffraction pattern of obtained metal-displacedlithium-titanium oxides of ramsdellite type, the oxides of Examples 3and 4 were found to show a single phase of the ramsdellite type crystalstructure.

Examples 5 and 6

In Examples 5 and 6, metal-displaced lithium-titanium oxides of theramsdellite type structure expressed by the formula (1) were synthesizedby varying the element ratio of Li:Ti:M^(VI).

That is, in Example 5, lithium carbonate (Li₂CO₃), titanium dioxide(TiO₂), and molybdenum trioxide (MoO₃), or tungsten trioxide (WO₃) wereblended at an element ratio Li:Ti:M^(VI) of x=0.5, y=0.5, and mixed for1 hour in a ball mill. In Example 6, lithium carbonate (Li₂CO₃),titanium dioxide (TiO₂), and molybdenum trioxide (MoO₃) or tungstentrioxide (WO₃) were blended at an element ratio Li:Ti:M^(VI) of x=1.0,y=1.0, and mixed for 1 hour in a ball mill. At this time, by addinglithium carbonate about 5% more than the element ratio, the loss bybaking process was compensated. In a muffle electric furnace, thematerials were calcined in atmosphere, for 2 hours at 650° C., and for12 hours at 800° C. The obtained mixed powder was mixed again in a ballmill for 1 hour, baked for 12 hours at 1100° C., and pulverized again.The obtained powder was compacted by a uniaxial pressure moldingmachine, and pelletized. The obtained pellets were similarly baked for36 hours at 1100° C. To obtain a ramsdellite structure reliably, thepellets were quenched from the baking temperature to room temperature.In the quenching process, the liquid nitrogen was used as in Examples 1and 2.

From the powder X-ray diffraction pattern of the obtainedmetal-displaced lithium-titanium oxides of ramsdellite type, the oxideof Example 5 was found to show a single phase of the ramsdellite typecrystal structure. On the other hand, the oxide of Example 6 was foundto contain an impurity phase in addition to the ramsdellite phase.

Comparative Example 1

In Comparative Example 1, known metal-nondisplaced lithium-titaniumoxide compound of the ramsdellite type structure expressed by theformula Li_(16/7)Ti_(24/7)O₈ (that is, Li₂Ti₃O₇) was synthesized.

That is, lithium carbonate (Li₂CO₃) and titanium dioxide (TiO₂) wereblended at an element ratio Li:Ti of 2:3, and mixed for 1 hour in a ballmill. At this time, by adding lithium carbonate about 5% more than theelement ratio, the loss by baking process was compensated. In a muffleelectric furnace, the materials were calcined in atmosphere, for 2 hoursat 650° C., and for 12 hours at 800° C. The obtained mixed powder wasmixed again in a ball mill for 1 hour, baked for 12 hours at 1100° C.,and pulverized again. The obtained powder was compacted by a uniaxialpressure molding machine, and pelletized. The obtained pellets weresimilarly baked for 36 hours at 1100° C. To obtain a ramsdellitestructure reliably, the pellets were quenched from the bakingtemperature to room temperature.

From the powder X-ray diffraction pattern of the obtained titanium oxidecompound of ramsdellite type, the oxide of Comparative Example 1 wasfound to show a single phase of the known ramsdellite type crystalstructure.

Comparative Example 2

In Comparative Example 2, tin-displaced lithium-titanium oxide oframsdellite type structure expressed by the formulaLi_(16/7)Ti_((24/7)-y)Sn_(y)O₈ was synthesized.

That is, lithium carbonate (Li₂CO₃), titanium dioxide (TiO₂), and tindioxide (SnO₂) were blended at an element ratio Li:Ti:Sn of 2:2.9:0.1,that is, y=0.1, and mixed for 1 hour in a ball mill. At this time, byadding lithium carbonate about 5% more than the element ratio, the lossby baking process was compensated. In a muffle electric furnace, thematerials were calcined in atmosphere, for 2 hours at 650° C., and for12 hours at 800° C. The obtained mixed powder was mixed again in a ballmill for 1 hour, baked for 12 hours at 1100° C., and pulverized again.The obtained powder was compacted by a uniaxial pressure moldingmachine, and pelletized. The obtained pellets were similarly baked for36 hours at 1100° C. To obtain a ramsdellite structure reliably, thepellets were quenched from the baking temperature to room temperature.

From the powder X-ray diffraction pattern of the obtained titanium oxidecompound of ramsdellite type, the oxide of Comparative Example 2 wasfound to show a single phase of the ramsdellite type crystal structure.

<Measurement of Lithium Ion Conductivity>

Diffusion performance of lithium is almost entirely dominated by lithiumion conductivity except for thermal diffusion. To measure the lithiumion conductivity of the ramsdellite type oxides synthesized in Examples1 to 6 and Comparative Examples 1 and 2, the oxides were baked intopellets, metal electrodes were sputtered on both sides of the obtainedpellet samples, and alternating-current impedance was measured by an ionblocking method. It was measured in the condition of applied voltage of10 mV, frequency range of 5 Hz to 13 MHz, and temperature of 25° C. Byfitting by using an equivalent circuit from the obtained Nyquistdiagram, the lithium ion conductivity of a bulk portion wasinvestigated.

Table 1 shows the results of ratio of lithium ion conductivity inExamples 1 to 6 and Comparative Example 2 on the basis of a referencevalue of 1.00 of known ramsdellite type oxide Li₂Ti₃O₇ (ComparativeExample 1). As is known from the results, the oxides of Examples 1, 2, 3and 4 were higher in lithium ion conductivity than the oxide ofComparative Example 1. The oxides of Examples 5 and 6 were higher inlithium ion conductivity than the oxide of Comparative Example 1.However, the oxide of Example 6 was reduced in lithium ion quantity, andwas lower in lithium ion conductivity than the oxide of Example 5. Theoxide of Comparative Example 2 was much lower in lithium ionconductivity than the oxide of Comparative Example 1.

These results suggested that the oxides of Examples 1 to 6 had a highlithium ion conductivity, and are excellent in lithium ion diffusion inthe solid matter. This is considered to be the effect of displacing partof Ti with M of higher valency, thereby generating hole sites anddecreasing the bonding strength of Li—O.

TABLE 1 Ratio of Li ion conductivity in bulk Example 1 1.51 Example 21.45 Example 3 1.26 Example 4 1.15 Example 5 1.20 Example 6 1.05Comparative 1.00 Example 1 Comparative 0.90 Example 2

<Fabrication of Electrochemical Measuring Cell (Half-cell)>

In the powder of the synthesized oxide, polytetrafluoroethylene wasmixed by 10 wt % as binder, and acetylene black by 30 wt % as conductiveagent, and mixed in a solvent to obtain a dispersed matter. Thedispersed matter was applied on one principal plane of an aluminum basematerial, and dried, pressurized and formed, and an operating electrodewas fabricated. To evaluate electrochemical intercalation anddeintercalation of lithium ions, a metal lithium foil was used as acounter-electrode of the operating electrode to fabricate and ahalf-cell (electrochemical measuring cell), which was used in thefollowing evaluation.

In this measuring cell, since the lithium metal is used ascounter-electrode, the electrode potential of the operating electrode isnoble as compared with the counter-electrode. Accordingly, the polarityis inverted compared to the case where the operating electrode is usedas the negative electrode of the whole cell. To avoid this confusion, inthe measuring cell (half-cell), the direction of intercalating thelithium ion into the operating electrode is called “charging,” and thedirection of deintercalating is called “discharging.” The nonaqueouselectrolyte solution was prepared by dissolving lithiumhexafluorophosphate in propylene carbonate solvent at a concentration of1M.

<Evaluation of Charging and Discharging Characteristic>

Using this electrochemical measuring cell, the battery was charged anddischarged in a potential range of 0.5V to 2.5V by reference to a metallithium electrode. In a thermostatic oven kept at room temperature of25° C., the battery was charged and discharged at an equivalent of 0.2C. Herein, 1 C is the current value required to discharge a single cellcompletely in 1 hour, and for the sake of convenience, the numericalvalue of nominal capacity of a single cell may be called 1C currentvalue. Therefore, 0.2 C is the current value required to discharge thenominal capacity in 5 hours.

FIG. 19 shows characteristic diagrams of charging curves E11, E21, E31,E41, C11, C21, and discharging curves E12, E22, E32, E42, C12, C22 ofExamples 1 to 6 and Comparative Examples 1 and 2. These charging anddischarging curves were obtained in the following process. Operatingelectrodes were fabricated by using the oxides of Examples 1 to 6 andComparative Examples 1 and 2, and the obtained operating electrodes wereassembled in electrochemical measuring cells. These electrochemicalmeasuring cells were charged in the specified condition to obtain andcharging curves, and the electrochemical measuring cells were dischargedin the specified condition to obtain discharging curves.

From these charging and discharging curves E11 to E41, E12 to E42, theoperating electrodes of Examples 1 to 6 were confirmed to have anaverage operating voltage of about 1.5V equivalent to voltage derivedfrom titanium oxidation and reduction, and a flat potential wasrecognized.

From the charging curves E31 and E41, in Example 3 (M=Mo) and Example 4(M=W) containing hexavalent metal oxide, a small flat potential ofsecond stage corresponding to reduction of displacing element (decreaseof valency) was recognized in the terminal stage of charging. That is,when lithium ion (monovalent) gets into a three-dimensional skeleton ofa crystal, in order to maintain the electrical neutrality of the entirecrystal, not only is the titanium ion (tetravalent) reduced, but alsothe displacing element M is changed from hexavalent to pentavalent form,which is estimated to express a small flat potential of the secondstage.

In discharge capacity of the operating electrodes using the oxides ofExamples 1 to 6 and Comparative Examples 1 and 2, the electrode weightcapacity density (mAh/g) was calculated, and on the basis of referencevalue (1.00) of Comparative Example 1, the discharge capacity ratio ofExamples 1 to 6 and Comparative Example 2 is shown in Table 2. Accordingto the result, Example 1 was increased in discharge capacity by 8% ascompared with Comparative Example 1, and Example 2 was increased indischarge capacity by as much as 21% as compared with ComparativeExample 1. This is considered to be the result of increasing effect ofhole quantity at tunnel site by displacement of element M of highervalency (pentavalent or hexavalent) into Ti site.

In discharge capacity of Examples 5 and 6, similarly, the electrodeweight capacity density (mAh/g) was calculated, and on the basis ofreference value (1.00) of Comparative Example 1, the discharge capacityratio was calculated and the results are in Table 2. The electrodeweight capacity density (mAh/g) mentioned herein is discharge capacityper unit weight of the electrode. The discharge capacity ratio is theratio of the measured discharge capacity to the reference value ofdischarge capacity. In Example 6 (x=y=1.0), since the electrode weightcapacity density is decreased due to presence of impurity phase, thedischarge capacity ratio is lower (0.65) than that in ComparativeExample 1. This is because the impurity phase does not contribute tocharge and discharge. By evaluating comprehensively these results andthe results of lithium ion conductivity, each range of x and y isdesired to be 0.5 or less.

TABLE 2 Discharge capacity ratio Example 1 1.08 Example 2 1.21 Example 31.12 Example 4 1.17 Example 5 1.02 Example 6 0.65 Comparative 1.00Example 1 Comparative 0.85 Example 2

<Evaluation of Discharge Rate Characteristics>

In the operating electrodes manufactured the oxides of Examples 1 to 4and Comparative Examples 1 and 2, the current value was raised atelevating steps, and the rate characteristics were tested. Withreference to metal lithium electrode, the batteries were charged anddischarged in the potential range of 0.5V to 2.5V. By varying thedischarge rate to 0.2 C, 0.5 C, and 1 C, measuring cells of Examples 1to 4 and Comparative Examples 1 and 2 were discharged, and the dischargecapacity was measured. The results are shown in Table 3. The dischargecapacity ratio when discharged at a rate of 0.2 C is indicated asreference value 1.0. In Examples 1, 2, 3, and 4, the discharge capacitywas maintained higher than in Comparative Example 1. Hence, the oxidecompounds of the invention are also confirmed to be suited to fastcharging and discharging. On the other hand, the discharge capacityratio of Comparative Example 2 was lowest in all the Examples andComparative Examples.

TABLE 3 Discharge rate 0.2c 0.5c 1.0c Discharge capacity ratio Example 11.0 0.93 0.89 Example 2 1.0 0.95 0.86 Example 3 1.0 0.85 0.80 Example 41.0 0.83 0.78 Comparative 1.0 0.81 0.71 Example 1 Comparative 1.0 0.650.45 Example 2

The invention hence provides a negative electrode active material and anonaqueous electrolyte battery excellent in fast charging anddischarging performance and repeated charging and dischargingperformance, and further provides a small-sized battery pack havingbatteries of such excellent performances, and a small-sized vehiclehaving such battery pack.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A negative electrode active material, comprising a metal-displaced lithium-titanium oxide of a ramsdellite structure expressed by the formula (1): Li_((16/7)-x)Ti_((24/7)-y)M_(y)O₈  (1) where M is at least one metal element selected from the group consisting of Nb, Ta, Mo, and W, and x and y are respectively numbers in the range of 0<x<16/7 and 0<y<24/7.
 2. The material according to claim 1, wherein the x and y are in the range of 0<x≦2.0, and 0<y≦2.0, respectively.
 3. The material according to claim 2, wherein the x and y are in the range of 0<x≦0.5, and 0<y≦0.5, respectively.
 4. The material according to claim 1, wherein the metal-displaced lithium-titanium oxide has a crystal system of a space group represented by Pnma.
 5. A nonaqueous electrolyte battery comprising: a negative electrode comprising a negative electrode active material; a positive electrode; a nonaqueous electrolyte interposed between the negative electrode and positive electrode; and a battery container which accommodates the negative electrode, the positive electrode, and the nonaqueous electrolyte, wherein the negative electrode active material comprises a metal-displaced lithium-titanium oxide of a ramsdellite structure expressed by the formula (1): Li_((16/7)-x)Ti_((24/7)-y)M_(y)O₈  (1) where M is at least one metal element selected from the group consisting of Nb, Ta, Mo, and W, and x and y are respectively numbers in the range of 0<x<16/7 and 0<y<24/7.
 6. The battery according to claim 5, wherein the x and y are in the range of 0<x≦2.0, and 0<y≦2.0, respectively.
 7. The battery according to claim 6, wherein the x and y are in the range of 0<x≦0.5, and 0<y≦0.5, respectively.
 8. The battery according to claim 5, wherein the metal-displaced lithium-titanium oxide has a crystal system of a space group represented by Pnma.
 9. The battery according to claim 5, wherein the negative electrode active material has an average particle size of 1 μm or less.
 10. A battery pack comprising: a battery module comprising a plurality of nonaqueous electrolyte batteries connected in series; and a pack container which accommodates the battery module, wherein the nonaqueous electrolyte batteries comprise: a negative electrode active material comprising a metal-displaced lithium-titanium oxide of a ramsdellite structure expressed by the formula (1): Li_((16/7)-x)Ti_((24/7)-y)M_(y)O₈  (1) where M is at least one metal element selected from the group consisting of Nb, Ta, Mo, and W, and x and y are respectively numbers in the range of 0<x<16/7 and 0<y<24/7; a negative electrode comprising the negative electrode active material; a positive electrode; a nonaqueous electrolyte interposed between the negative electrode and positive electrode; and a battery container which accommodates the negative electrode, the positive electrode, and the nonaqueous electrolyte.
 11. The battery pack according to claim 10, wherein the x and y are in the range of 0<x≦2.0, and 0<y≦2.0, respectively.
 12. The battery pack according to claim 11, wherein the x and y are in the range of 0<x≦0.5, and 0<y≦0.5, respectively.
 13. The battery pack according to claim 10, wherein the metal-displaced lithium-titanium oxide has a crystal system of a space group represented by Pnma.
 14. The battery pack according to claim 10, wherein the negative electrode active material has an average particle size of 1 μm or less.
 15. A vehicle comprising: an internal combustion engine; a motor; wheels driven by at least one of the internal combustion engine and the motor; a battery pack which supplies electricity to the motor; and a generator which charges the battery pack by supplying electric power generated by a rotating force of the wheels to the battery pack, wherein the battery pack comprises: a battery module comprising a plurality of nonaqueous electrolyte batteries connected in series; and a pack container which accommodates the battery module, and the nonaqueous electrolyte batteries comprise: a negative electrode active material comprising a metal-displaced lithium-titanium oxide of a ramsdellite structure expressed by the formula (1): Li_((16/7)-x)Ti_((24/7)-y)M_(y)O₈  (1) where M is at least one metal element selected from the group consisting of Nb, Ta, Mo, and W, and x and y are respectively numbers in the range of 0<x<16/7 and 0<y<24/7; a negative electrode comprising the negative electrode active material; a positive electrode; a nonaqueous electrolyte interposed between the negative electrode and positive electrode; and a battery container which accommodates the negative electrode, the positive electrode, and the nonaqueous electrolyte.
 16. The vehicle according to claim 15, wherein the x and y are in the range of 0<x≦2.0, and 0<y≦2.0, respectively.
 17. The vehicle according to claim 16, wherein the x and y are in the range of 0<x≦0.5, and 0<y≦0.5, respectively.
 18. The vehicle according to claim 15, wherein the metal-displaced lithium-titanium oxide has a crystal system of a space group represented by Pnma.
 19. The vehicle according to claim 15, wherein the negative electrode active material has an average particle size of 1 μm or less. 